The present invention relates to a process for recovering shale-oil in situ. A section in an oil-shale deposit is fractured and heated to a temperature from about 360.degree. C. to about 475.degree. C. The resulting rubble, or fractured oil-shale, is then cooled to a temperature below the boiling point of water at the operating pressure and then contacted with a microemulsion which extracts and absorbs shale-oil. The microemulsion is then brought to the surface and a substantial fraction of shale-oil is recovered therefrom.
Oil-shale, one of the leading sources under investigation for the production of synthetic fuels, may play a leading role in the energy future of the United States. The primary reason for the growing importance of oil-shale, as well as coal, is the rapid depletion of known petroleum and natural gas reserves. These known reserves are being depleted at a faster rate than the rate of discovering new reserves. As the era of petroleum growth draws to a close, the world's energy mix will have to change. Transition energy sources will be needed as a bridge between petroleum and the potentially unlimited energy sources of the future; such sources being, for example, solar power and nuclear fusion. Owing to their great abundance, coal and oil-shale are perceived as the keystones of such a bridge. Consequently, a great deal of research and development is presently in progress to provide economical ways of converting these solid resources to valuable liquids and gases.
Although most conventional processes for recovering oil from oil-shale involve the mining and retorting of oil-shale, there is a considerable amount of interest in, in place or in situ processing in order to eliminate a substantial portion of the mining and handling costs associated with conventional processes.
Furthermore, in situ processes may be applicable to deposits of various thicknesses, grades, and amounts of overburden that are not readily amenable to mining. In addition, it eliminates the necessity of disposing of large quantities of spent shale.
In general, conventional in situ processes for obtaining oil from oil-shale comprises drilling wells having a predetermined pattern into the oil-shale formation, fracturing to create permeability, or rubble, igniting the shale in one or more of the wells, pumping air down the ignition well to support combustion, forcing hot combustion gases through the oil-shale to convert solid organic matter of the shale into oil, and recovering the oil thus generated from other wells in the pattern. Conventional fracturing techniques include hydraulic pressure, chemical explosives, and nuclear explosives. Although such in situ processes have been in the testing stages for at least about 20 years, they are generally ineffective and result in a relatively low oil recovery.